While these studies certainly point to a
plausible relation between galaxy interaction and the formation of SSCs, one
must be careful in drawing any direct, causal connection between the two
processes. The cases cited above by no means represent an unbiased sample; in
fact, they were, to a large extent, selected based on prior knowledge
of their extreme characteristics. It is well known that galaxy interactions
can give rise to intense starburst activity (see contributions in
Shlosman 1994).
Similarly, W-R galaxies are among the earliest and most
vigorous manifestations of starbursts
(Conti 1991;
Vacca & Conti 1992).
Thus, an equally viable interpretation is that cluster formation is an
integral part of star formation in starbursts in general. In as much as
galaxy interactions can trigger starbursts, there is a high likelihood of
finding SSCs in interacting systems; but such an association is indirect -
interactions are sufficient but not necessary for cluster formation. That
SSCs are also found in galaxies that are not obviously interacting
(O'Connell et al. 1994;
Meurer et al. 1995)
supports this viewpoint, as does the
tendency for some SSCs to be located in circumnuclear rings and other
relatively quiescent environments, as will be described below.